As soft magnetic materials used for various types of transformers, various types of reactors, choke coils, noise control components, laser power sources, pulse power magnetic components for accelerators, and the like, there are known silicon steels, ferrites, amorphous alloys, nanocrystalline alloys and the like.
However, since ferrite materials have problems of having a low saturation magnetic flux density and poor temperature characteristics, they are unsuitable for applications of high powers such as coil components for high-capacity inverters and power sources, and distribution transformers because they easily saturate magnetically. Although silicon steel plates are inexpensive in terms of their materials and have a high magnetic flux density, but they have a problem of exhibiting a high magnetic core loss for high-frequency applications.
On the other hand, amorphous alloys are generally manufactured by quenching raw materials from a liquid phase or a gas phase. Therefore, it is known that since Fe-based and Co-based amorphous alloys have no crystal grains, they intrinsically exhibit no crystal magnetic anisotropy and exhibit excellent soft magnetic properties. Hence, Fe-based and Co-based amorphous alloys are used for power transformer iron cores, choke coils, magnetic heads, current sensors and the like.
It is known that nanocrystalline alloys exhibit excellent soft magnetic properties comparable to Co-based amorphous alloys and a high saturation magnetic flux density comparable to Fe-based amorphous alloys, and are used for magnetic cores for common-mode choke coils, high-frequency transformers, pulse transformers and the like.
As the representative compositions, there are known Fe—Cu—(Nb, Ti, Zr, Hf, Mo, W, Ta)—Si—B alloys, Fe—Cu—(Nb, Ti, Zr, Hf, Mo, W, Ta)—B alloys cited in Patent Document 1 and Patent Document 2, and the like. These Fe-based nanocrystalline alloys are fabricated by annealing amorphous alloys prepared by rapid quenching technique from a melt or gas phase to microcrystallize them. As methods for quenching from a liquid melt phase, there are known a single roll method, a twin roll method, a centrifugal quenching method, an in-rotating liquid spinning method, an atomizing method, a cavitation method, and the like. As methods for quenching from a gas phase, there are known a sputter method, a vapor deposition method, an ion plating method, and the like. Fe-based nanocrystalline alloys are ones obtained by microcrystallizing amorphous alloys fabricated by these methods, and have almost no thermal instability, which is seen in amorphous alloys, and are known to exhibit excellent soft magnetic properties having a high saturation magnetic flux density in the same levels as in Fe-based amorphous alloys and low magnetostriction. Further, nanocrystalline alloys are known to exhibit little change over time and to be excellent in temperature characteristics.
Patent Document 3 studies such an Fe-based nanocrystalline alloy as described above, and discloses, for example, a soft magnetic ribbon in which the Fe atom concentration is higher at a position deeper than 10 nm from the surface in terms of SiO2 than the oxygen atom concentration, and the Cu atom concentration is locally raised at a position deeper than 5 nm from the surface.
Patent Document 4 also describes that, as a technique to work an amorphous alloy ribbon, the workability is raised by addition of C, P, S elements and the like to an alloy composition.    Patent Document 1: JP 04-4393 B    Patent Document 2: JP 01-242755 A    Patent Document 3: JP 2002-75718 A    Patent Document 4: JP 2006-316348 A